Air pressure control apparatus for surface hydraulic pumps



Dec. 13, 1955 R. H. DErrRxcKsoN AIR PRESSURE CONTROL APPARATUS F OR SURFACE HYDRAULIC PUMPS Filed May l5, 1953 2 Sheets-Sheet l @QQQQW Engis!! Dec. 13, 1955 R, H. Dx-:rrRlcKsoN AIR PRESSURE CONTROL APPARATUS FOR SURFACE HYDRAULIC PUMPS 2 Sheets-Sheet 2 Filed May 15, 1955 SPRAY (onPREssDR NUZZLE g;

ou.. LEVEL. (MAX) HEAT sm-HANGER TO SUM? United States Patent AIR PRESSURE CONTROL APPARATUS FOR SURFACE HYDRAULIC PUMPS Roy H. Deitricltson, Toledo, Ohio, assigner to The llational Supply Company, Pittsburgh, Pa., a corporation of Pennsylvania Application May 13, 1953, Serial No. 354,689

9 Claims. (Cl. 60-51) This invention relates to hydraulically actuated surface equipment for well pumps of the type frequently used in oil wells and, more particularly, to a hydraulic system by which a surface jack is activated for the vertical reciprocation of a pumping rod extending into a deep well, for example, an oil well.

A surface hydraulic apparatus includes a iluid motor or jack in which there is located a piston that is connected to a pump rod which usually extends downwardly from the pumping jack and is operatively linked to the sucker rod string extending down to the pump itself at the production area level. A hydraulic system for the introduction of working fluid under high pressure into the pumping jack to force the piston upwardly usually includes a main pump and an engine for driving the pump, a sump for providing a supply of working fluid, a so-called counterbalancing tank in which a volume of working fluid is kept under pressure for the storage of energy so that the load on the pump engine can be kept relatively constant during both up and down strokes and the necessary controls, valves and hydraulic lines properly to connect one part of the apparatus with the others.

In a system of this general type various control means must be provided for automatically controlling the connections between the various elements, the operation of the pump, and the proper pressures and volumes of both the working iluid and air within the system.

The instant invention has as its principal object the provision of automatic air pressure control means for controlling the pressure within the counterbalancing tank to compensate for the variations in such pressure resulting from variations in the volume of iluid in the tank and the temperature of the tank due to atmospheric temperature changes.

It is another object of this invention to provide air pressure control means for the counterbalancing tank of a surface hydraulic system having pressure actuated control means normally operative to control an air compressor employed to maintain the air pressure within the tank and provided with auxiliary means for bleeding air from the tank when the pressure therein rises above the normal operating level, said auxiliary means operating only after the air compressor control means has operated.

It is still another object of this invention to provide air pressure control means for the counterbalancing tank of a surface hydraulic system incorporating a relatively stable source of air pressure which follows the maximum pressure in the tank and not rapid iluctuations in tank pressure whereby lluttering of the air pressure control mechanisms is prevented.

Other and more specific objects and advantages of the invention will be better understood from the specification which follows and from the drawings, in which- Fig. 1 is a simplified view, in elevation and on a very small scale, of a surface hydraulic apparatus for actuating the sucker rod of a down well pump, certain parts being shown in section.

Patented Dec. 13, 1955 Fig. 2 is a schematic hydraulic diagram of the main apparatus and lines constituting a surface hydraulic system and in particular illustrating the portion of the apparatus embodying the instant invention for automatic air pressure control.

A surface hydraulic system embodying the invention includes a number of conventional structures, the operation of which the invention is designed to facilitate. A surface hydraulic apparatus is designed for the purpose of actuating a piston 10 of a fluid motor in its elongated motor cylinder 11 which may be erected upon suitable framework 12 extending vertically above a casing 13 of a well. A sucker rod 14 is attached to the piston 10 of the lluid motor and extends down the casing 13 where it is connected to the plunger of a pump (not shown) in the production area of the well. The pumping jack or iluid motor 11 is connected by a main pump line 15 to a main pump 16. The line 15 may be provided with an accumulator pipe 17 (see Fig. l-not shown in Fig. 2) for the purpose of reducing the peak sucker rod stresses by absorbing pulsations in the power oil beneath the piston 10.

The pump 16 is driven by a shaft 18 (Fig. 2) extending through a shaft tunnel 19 (Fig. 1) and connected by suitable clutch means (not shown) to an engine 20.

The pump 16 also is connected by a main tank line 21 to the bottom of a counterbalancing tank generally indicated at 22. The counterbalancing tank 22 is mounted upon legs 23 and provided with a' shut olf valve 24.

In addition to the main pump 16 the present system includes a constantly driven scavenging pump 25 which is connected by a scavenging pump output line 26 through an oil lter 27 and heat exchanger 28 to a tank return line 29. The tank return line 29 is attached to a spray nozzle 30 located at the top of the tank 22 and through which working fluid returned to the tank by the scavenging pump 25 is sprayed onto the interior surface of the tank 22. Spraying the working iluid onto the interior surface of the tank 22 at its top provides for thorough washing over the surface of the tank 22 so that the rust and oxidization inhibitors introduced into the working fluid may prevent corrosion and condensation on the inner surfaces of the tank 22.

The scavenging pump 25 has an input line 31 which is connected through an upwardly openable check valve 32 to a main sump 33. The top of the pumping jack 11 also is connected by a line 34 to the sump 33 so that leakage past the jack piston is returned to the sump. Since the hydraulic system operates under a substantial pressure as hereinafter described, leakage is bound to occur at various points, and it is the function of the scavenging pump to make up for these losses.

Anair compressor 35 is connected by a line 36 to the upper portion of the tank 22 and functions to maintain pressure within the tank 22.

In general, the apparatus operates as follows: During an up stroke the pressure maintained within the tank 22 forces working iluid through the line 21 to the main pump 16.y The pump 16 raises the pressure on the fluid and pumps itV through the main line 15 into the pumpingjack 11. The high pressure working fluid thus introduced into the pumping jack 11 beneath the piston ltlrforces the piston 10 upwardly lifting the sucker rod 14 and the column of production iluid located in the casing 13 or in the tubing (not shown) within the casing 13 and delivering a quantity of the production lluid to the top of the well and to the production fluid manifold (not shown) whence it is led to storage or further treatment.

Upon the completion of an up stroke caused by the introduction of high pressure working iluid beneath the pumping jack piston 10, suitable reversing `valves lare lCe f actuated and the tluid within the pumping jack 11 tlows back through the main line to the main pump 16 and then with higher pressure added by the main pump 16 is pumped back into the counterbalancing tank 22.

The pressure to be maintained within the counterbalancing tank 22 is calculated by the equation set forth below according to the work to be performed. If Pr is the unit pressure beneath the piston 10 created by the weight of the sucker rod 14, Ps is the unit pressure exerted on the piston 19 by the static head of the column of production fluid in the well tubing and Pc is the counterbalancing pressure to be applied by the counterbalancing tank 22, then For example, if the weight of the sucker rod 14 creates a pressure of 200 p. s. i. beneath the piston 10 and the weight of the column of production uid creates a similar pressure of 400 p. s. i., then 20O+=400 p. s. i.

the average pressure to be maintained within the counterbalancing tank 22.

The pressure within the tank 22 is controlled by con trolling the air pressure within the tank and such control is divided into two phases. First, the instant invention provides means for controlling the operation of the air compressor 35 so that it pumps air into the tank 22 only when necessary to build up the air pressure therein. Second, the instant invention includes automatically actuated means for dumping or venting the tank 22 for direct reduction of air pressure within the tank 22 when necesv sary, said last means being operated only when the tank pressure continues to rise even though air compressor 35 has been shut off.

An air pressure sensing line 37 is connected to the tank 22 and then divided into an air pressure delivery line 38 and an air pressure control line 39.

Since air pressure in the tank affects in some measure the iiuid level control devices, such devices will be described briey herein, although claims thereto are made only in my eopending application Serial No. 354,167, filed May l l, 1953. The line 38 is connected to a chamber 4% located above a diaphragm 41 in a fluid level control pilot valve 42. A chamber 43 beneath the diaphragm 41 is connected by a fluid level sensing line 44 to the counterbalancing tank 22 at the height of the maximum iiuid level desired in the tank 22. A pocket 45 in the pliot valve 42 located beneath the chamber 43 is con nected to the chamber 43 by a passageway 46. A diaphragm plunger 47 extends downwardly from the diaphragm 41 into the pocket 45 and its end acts as a valve for the connection of a uid pressure line 48.

The liuid pressure line 48 is branched with one branch 49 leading to a uid bleeder valve 50 and thence to a sump line 51 and the other branch 52 leading beneath a piston 53 in a uid dump valve 54. The dump valve 54 controls the connection between a fluid branch line 55 that is connected to the main uid tank line 21 and a scavenging pump input branch line 56 which is connected into the scavenging pump input line 31 above the check valve 32.

When the working fluid in the tank 22 reaches the height of the connection of the uid sensing line 44, line 44 fills and the head of uid therein flexes the diaphragm 41 upwardly against the air pressure in the chamber 40 and compressing a small spring 57 which is located above a diaphragm 41. This pulls the plunger 47 upwardly and connects the tiuid sensing line 44 to the line 48. Pressure of the fluid in the line 48 lifts the piston 53 opening the uid dump valve 54 and placing the lines 55 and 56 in direct communication. Thus when the level of working uid in the tank 22 rises above its desired maximum the scavenging pump is connected between the output side of the tank 22 and the input side thereof to directly recirculate the working fluid within the tank 22 without adding fluid from the sump 33.

When the level of working fluid in the tank 22 drops below the connection point of the vertical fluid sensing line 44, the fluid in the line 44, chamber 43, pocket 45 and line 48 is bled away through the bleeder valve 50 until its pressure lowers to a point where it first allows the diaphragm 41 to be moved downwardly by the combined air pressure in the chamber 40 and spring 57 and, second, where it allows a spring 58 to move the piston 53 downwardly cutting off communication between the scavenging pump 25 and the main tank line 21 so that the scavenging pump once again pumps fluid from the sump 33 through the check valve 32 and into the tank 22.

As previously noted the iiuid level control above described is claimed in my said copending application Serial No. 354,167. The present invention relates particularly to the air pressure control for the counterbalancing tank 22.

Because of the fact that the air pressure in the counterbalancing tank fluctuates rapidly as liquid rushes in and out during the operation of the pumping jack, provision must be made for operation of the air compressor 35 in response to some much more stable pressure. For this purpose the present invention provides an air chamber 70 connected to the counterbalancing tank through the control line 39 and an outwardly opening check valve 68. Thus the air chamber will reach a pressure corresponding to the maximum pressure in the tank. However, a bleed valve 66 is connected to the line 39 on the chamber side of the check valve 68 so that the pressure in the air chamber is reduced at a controlled rate, and will thus follow a reduction in maximum tank pressure if one occurs. The air chamber 70 will be supplied with air from the counterbalancing tank each time the pressure in the tank exceeds the existing pressure in the air chamber so that check valve 68 opens. During the remainder of the time check valve 68 is held closed by the pressure in the air chamber.

The air pressure control line 39 connects to two spring loaded air pressure sensing valves through branch lines. The rst sensing valve is designated generally 63 and connects to a branch line 62. The sensing valve 63 has a plunger 64, a valve head 65 and a biasing spring 66 which normally urges the valve head into engagement with a valve seat 67 so that branch line 62 is closed, and no air pressure can be communicated from line 62 to an outlet line 69.

When the pressure in the counterbalancing tank exceeds a predetermined maximum, which is, of course reected promptly in air chamber 70, valve 63 is opened and line 62 brought into communication with line 69 which disables the supplying compressor 35, either by unloading the compressor or by declutching it from its driving means in a manner well understood in the art. If the maximum pressure in the tank 22 at repeated cycles of operation of the jack falls below the pressure in air chamber 70, the bleed valve 60 will soon reduce the pressure in the air chamber to the point where it is insuiiicient to hold valve 65 open and the compressor will resume supplying air to the tank. Thus the present invention controls the operation of the compressor not by the rapidly fluctuating air pressure in the tank, but by the relatively steady pressure of the air chamber 70, reecting the maximum pressure in the counterbalancing tank reached in successive cycles of operation of the system.

A second branch line 71 connects the air control line 39 to a second air pressure sensing valve 72, in construction very much like the valve 63 and placed to connect the branch line 71 to the cylinder of an air dump valve 79 when open. The valve 72 has a plunger 73, a valve head 74 and a coil spring 75 biasing the valve against a seat 76 to close air line 71. The biasing spring of `this second valve is adjusted to a somewhat greater force than the spring of the first valve 63, so that a higher pressure (by for example 20 p. s. i.) is required to open it than is required to open the lirst valve. Thus, if shutting oi the supply of air to the tank is not effective to reduce the maximum pressure therein so that the pressure keeps on increasing, the pressure in the air chamber 70 and thus on valve 72 will likewise increase. Valve 72 is thus opened, and communication established between line 39, line 71, a line 77 to dump valve 79.

The dump valve 79 comprises a piston 78 having a valve extension 80 controlling an opening between a line 81 leading directly to the counterbalancing tank 22 and a vent line 82 leading back to the sump. A spring 83 biases the piston and valve to closed position.

When the dump Valve is opened by the admission of air past sensing valve head 74, air from the tank can iiow directly from the tank 22 to the sump. The maximum tank pressure is thus reduced rather quickly, more rapidly of course than can be expected from normal dissipation and leakage. As the air chamber pressure bleeds down through bleed valve 60 it soon reaches a point where sensing valve 72 closes, permitting the dump valve stem 30 to seat and stopping the rapid venting of air from the tank. It will be seen that the time required for the air chamber to bleed down, and thus the duration of the open period of the dump valve, is adjustable by the setting of the bleed valve 6i) and may be so arranged that air from the tank is dumped in large or small increments.

To recapitulate the operation of the parts described, air pressure is built up in tank 22 by compressor 35 which may be driven by any conventional means. During operation of the ptunping system, the air pressure in the tank varies at each stroke of the jack 11 because of the withdrawal and replacement of working iiuid. This pressure therefore uctuates between a minimum and a maximum at each stroke.

Whenever the pressure in the tank 22 exceeds the pressure in the air chamber 70, air passes check valve 68 and flows to the chamber. Thus only the maximum pressure of the tank has any signiiicant eiiect on the air chamber pressure.

When the air chamber pressure reaches a predetermined value, valve 63 first opens to stop or unload the compresser. This expedient may not be enough to cause the maximum tank pressure to drop. For example, if the system has been operating during a cool night, the air pressure will rise as the day becomes warmer and the rays of the sun strike the tank. If the maximum pressure continues to rise even with the compressor effectively stopped, the pressure in air chamber 70 will also rise to the point where the second sensing valve 72 opens, thus opening dump Valve 79 and discharging air from the tank directly through lines 81 and 82 to the sump. Discharge is made to the sump because it is not desired simply to vent the tank to atmosphere since the entrained oil in the air would dissipate over all of the surrounding equipment and might also create a fire hazard.

While the invention has been disclosed in conjunction with a specific installation it should be expressly understood that it is capable of numerous embodiments Without departing from the scope of the appended claims.

What I claim is:

1. In a hydraulic system for operating a fluid motor piston, a counterbalancing tank containing liquid under air pressure which fluctuates between a minimum and maximum at each piston stroke, an air compressor connected to supply air to said tank, means to control the maximum tank air pressure comprising, an air chamber, means to charge said air chamber from said tank to a relatively stable pressure corresponding substantially to the maximum air pressure in said tank, means responsive to a predetermined pressure in said air chamber to disable said air compressor, and means to reduce the pressure in said air chamber at a controlled rate.

2. In ahydraulic system for operating a uid motor piston, a counterbalancing tank containing liquid under air pressure which iluctuates between a minimum and maximum at each piston stroke, an air compressor connected to supply air to said tank, means to control the maximum tank air pressure comprising, an air chamber, means to charge said air chamber from said tank to a relatively stable pressure corresponding substantially to the maximum air pressure in said tank, first means responsive to a predetermined pressure in said air chamber to disable said air compressor, second means responsive to a higher air pressure in said air chamber to vent said tank, and means to reduce the pressure in said air chamber at a controlled rate.

3. In a hydraulic system for operating a iiuid motor piston, a counterbalancing tank containing liquid under air pressure which iluctuates between a minimum and maximum at each piston stroke, an air compressor connected to supply air to said tank, means to control the maximum tank air pressure comprising, an air chamber, means to charge said air chamber from said tank to a relatively stable pressure reflecting the maximum air pressure in said tank, means responsive to a predetermined pressure in said air chamber to disable said air compressor, and means to reduce the pressure in said air chamber at a controlled rate.

4. In a hydraulic system for operating a uid motor piston, a counterbalancing tank containing liquid under air pressure which iluctuates between a minimum and maximum at each piston stroke, an air compressor connected to supply air to said tank, means to control the maximum tank air pressure comprising, an air chamber, a connection from said tank to said air chamber, a check valve in said connection whereby said air chamber is charged to a relatively stable pressure corresponding substantially to the maximum air pressure in said tank, means responsive to a predetermined pressure in said air chamber to disable said air compressor, and means to reduce the pressure in said air chamber at a controlled rate.

5. In a hydraulic system for operating a fluid motor piston, a counterbalancing tank containing liquid under air pressure which liuctuates between a minimum and maximum at each piston stroke, an air compressor connected to supply air to said tank, means to control the maximum tank air pressure comprising an air chamber, means to charge said air chamber from said tank to a relatively stable pressure corresponding substantially to the maximum air pressure in said tank, first means responsive to a predetermined pressure in said air chamber to disable said air compressor, a pneumatically actuated vent valve connected to said tank, second means responsive to a higher air pressure in said chamber to cause actuation of said vent valve, and means to reduce the pressure in said air chamber at a controlled rate.

6. In a hydraulic system for operating a fluid motor piston, a counterbalancing tank containing liquid under air pressure which iiuctuates between a minimum and maximum at each piston stroke, an air compressor connected to supply air to said tank, means to control the maximum tank air pressure comprising, an air chamber, a iirst pressure responsive means, a second pressure responsive means, a check valve, a connection from said tank to said check valve, parallel connections from said check valve to said air chamber and said first and second pressure responsive means, means controlled by said first pressure responsive means for disabling said air compressor when said air chamber pressure reaches a predetermined value, other means controlled by said second pressure responsive means to vent said tank, and a bleed valve connected to reduce the pressure in said air chamber at a controlled rate.

7. Apparatus to control air pressure in a tank in which the air pressure iiuctuates relatively rapidly comprising, an air compressor connected to supply air to said tank, an air chamber, means to charge said air chamber from said tank to a relatively stable pressure corresponding substantially to the maximum air pressure in said tank,

7 means responsive to a predetermined pressure in said air chamber to disable said air compressor, and means to reduce the pressure in said air chamber at a controlled rate.

8. Apparatus to control air pressure in a tank in which the air pressure uctuates relatively rapidly comprising, an air compressor connected to supply air to said tank, an air chamber, means to charge said air chamber from said tank to a relatively stable pressure reliecting the maximum air pressure in said tank, means responsive to a predetermined pressure in said air chamber to disable said air compressor, and means to reduce the pressure in said air chamber at a controlled rate.

9. Apparatus to control air pressure in a tank in which the air pressure uctuates relatively rapidly comprising,

an air compressor connected to supply air to said tank, an air chamber, a connection from said tank to said air chamber, a check valve in said connection whereby said air chamber is charged to a relatively stable pressure corresponding substantially to the maximum air pressure in said tank, means responsive to a predetermined pressure in said air chamber to disable said air compressor, and means to reduce the pressure in said air chamber at a controlled rate.

References Cited in the tile of this patent UNITED STATES PATENTS 2,347,302 Twyman et al Apr. 25, 1944 2,560,676 White July 17, 1951 2,665,551 Chenault Jan. 12, 1954 

